Industrial-rated circuit breakers are available having operating components that are designed for automatic assembly to provide cost improvement as well as improved operating efficiency. The precision alignment performed by the automated assembly equipment allows the operating components within the circuit breaker operation mechanism to be installed within very close operating tolerances. The operating mechanism assembly includes a pair of powerful operating springs that are overcentered for rapidly driving the movable contact arm and the attached movable contact away from the stationary fixed contact to interrupt the circuit current. The operating mechanism includes a cradle operator which engages a latch assembly to prevent the movable contact arm from being driven to its open position under the urgence of the charged operating springs. The compact latch assembly includes a primary and secondary latch operating within a common support structure.
With higher ampere-rated industrial circuit breaker designs in the range of 1200 ampere continuous current carrying capacity, the correspondingly larger operating springs provide a substantially increased holding force to the circuit breaker contacts such that a correspondingly larger force is required to manually separate the circuit breaker contacts to reset and close the operating mechanism. The increased current transfer through the compact circuit breaker enclosure during overcurrent conditions produces an arc upon contact separation that is difficult to quench and deionize within the close confines of the correspondingly compact arc chamber.
The increased temperature generated within the compact circuit breaker enclosure during circuit interruption heats up several of the current-carrying components such as the movable contact and movable contact arm whereby additional thermal insulating means are required to prevent damage to the lower-temperature materials used within the circuit breaker enclosure.
The increased current creates a correspondingly increased arc that requires additional inter-phasal line lug baffles as well as additional electrical isolation between the electrical and electronic components within the circuit breaker enclosure.
One purpose of the instant invention accordingly is to provide a compact circuit breaker having sufficient capability to allow manual movement of the operating handle to reset and close the circuit breaker against the bias of the operating mechanism springs.
A second purpose of this invention is to provide supplemental arc extinguishing means to the compact circuit breaker enclosure to allow complete and rapid circuit interruption at the higher circuit ratings and to prevent the occurrence of inter-phasal faults exterior to the enclosure.
A still further purpose of the invention is to provide a compact circuit breaker having means for externally viewing the condition of the circuit breaker contacts.
An additional purpose of the invention is to allow the hot movable contact arm to impact against the bumper attached to the circuit breaker cover without melting the bumper.
A further additional purpose of the invention is to provide electrical isolation to the movable contact arm braid and to the current transformer pin connectors.